With an aid of an electron beam micro-column on the basis of a lens with a micro-size and an alignment principle, a scanning tunneling microscope, or an electron emitter operated under a micro-alignment positioner was introduced in the second half of the 1980's. In addition to small size and low manufacturing cost, the electron beam micro-column can form a finely concentrated electron beam, so that it improves the electron beam current and high resolution. Thus, it became widely used in the fields of micro-lithography and electron microscope.
The alignment principles used by a micro-column are similar to STMs in that a precision X-Y-Z positioner is used to control a location of a sharp tip, in the case of micro-column the location of the tip of electron emitter, and that the electrons emitted from the tip are used for controlling and measuring the location of the tip.
FIG. 1 is an exploded diagram of an electron emitter 110 and electron optical column 120. The electron emitter 110 includes an electron emitter tip 112, which may be a Zr/O/W Schottky electron emitter tip, such as A single crystal tungsten, hafnium carbide or diamond tip. The electron emitter tip 112 is mounted on a miniature three-axis micro-positioner 114. Micropositioner 114 has a range of movement in the order of tens of micrometers to more than 1 mm in each of the X-Y-Z directions and has sub-nanometer positioning capability. Micropositioner 114 is used to align the electron emitter tip 112 with electron optical column 120. Typical dimensions of miniature the axis micro-positioner 114 are approximately 2×2×1.1 cm.
The typical components of electron optical column 120 include a micro-source lens 122 with an extractor 124 and an anode 128 with apertures of approximately a few micrometers and 100 micrometer in diameter, respectively. The extractor 124 as an extraction electrode is fabricated from a few˜a few hundred micrometers thick silicon (Si) membrane with a bore diameter of a few microns. For an optimum lense operation, the electron emitter tip 112 is required to be positioned very closely and precisely aligned to extractor hole 126.
Due to the proximity of emitter source 110 to extractor 124, aligning electron emitter tip 112 to extractor hole 126 is difficult. The problem is exacerbated by the dimension of extractor hole 126 and the overall column dimension. For fine alignment, an STM-type X-Y positioner has been used in vacuum state to scan the tip over the extractor electrode. However, because the location of the electron emitter tip is not easily and precisely measured, this approach requires so much time for alignment with the extractor hole.
Accordingly, there is need for a method to easily and precisely align an electron emitter and an extractor hole of a micro-column. In this regard, International patent application PCT/US1999/25430 proposed the alignment method. However, because the proposed application makes use of four V-grooves for performing the alignment, it requires additional components for precise alignment within a vacuum space, even if such components are exempted out of the vacuum space.
Further, as the alignment between the electron emitter and the extractor hole may be changed after a long use of the micro-column, it is very difficult to sense such change of alignment.
In case of the micro-column, since the object to be measured and/or aligned is very small and requires precise measurement and alignment, it is necessary to repeat the measuring and/or aligning operation. Thus, it consumes time and cost for carrying out the measurement and alignment. Also, it is more difficult to determine and calibrate the assembled micro-column during the use.